Catalyst for alkylation of C4 -C5 isoparaffin by at least one C3 -C6 olefin

ABSTRACT

The present invention relates to a catalyst comprising silica and an acid phase comprising sulphuric acid and the compound HB(HSO 4 ) 4 , the silica having been impregnated by said acid phase, said catalyst being such that is consists essentially of particles of an average diameter of between 0.1 and 30 μm, prior to its impregnation with said acid phase, has a total porous volume of between 0.1 and 6 cm 3  per gram and said acid phase contains between 0.4% and 68.8% by weight of the compound HB(HSO 4 ) 4 , and between 31.2% and 99.6% by weight of the compound containing neither sulphuric anhydride nor boric acid. 
     The invention also relates to the preparation and use of said catalyst in catalytic alkylation of isobutane and/or isopentane in the presence of at least one olefin containing 3 to 6 carbon atoms per molecule.

BACKGROUND OF THE INVENTION

The present invention relates to a catalyst comprising silica and anacid phase containing sulphuric acid and the compound HB(HSO₄)₄, thesilica having been impregnated by said acid phase. The invention alsorelates to the preparation and use of said catalyst in catalyticalkylation of isoparaffin (isobutane and/or isopentane) in the presenceof at least one olefin containing 3 to 6 carbon atoms per molecule.

In order to supply internal combustion engines which have sparkignition, and particularly engines with a high compression ratio, it isparticularly advantageous to have fuels with high octane ratings, thatis to say consisting essentially of heavily branched paraffinhydrocarbons. The alkylation of isoparaffins (isobutane and/orisopentane) by at least one olefin containing 3 to 6 carbon atoms permolecule allows such products to be obtained. This reaction requires theuse of very acidic catalysts, particularly for reducing parasiticreactions such as hydride abstraction from the olefin and ofpolymerization which provide slightly branched hydrocarbons with a lowoctane rating and unsaturated hydrocarbons, cracking reactions anddismutation reactions.

The existing processes for production of hydrocarbons by alkylation ofisobutane by olefins generally use either sulphuric acid or hydrofluoricacid as the catalyst. In these processes the acid catalyst constitutes aliquid phase which is placed in contact with the liquidisobutane/olefin(s) mixture to form an emulsion. These processes areexpensive and give rise to significant problems with regard to personaland environmental safety. In order to remedy these problems, differentcatalytic systems of sulphuric acid and hydrofluoric acid in liquidphase have been sought.

In order to catalyze the alkylation reactions of isoparaffins byolefins, it has already been proposed to develop acid catalysts fromnumerous acid solids of different types. Amongst the families of acidcatalysts, molecular sieves, macroreticular resins, possibly associatedwith BF₃, Lewis and/or Bronsted acids deposited on various inorganicsupports, chlorous aluminiums, graphites interpenetrated with Lewisand/or Bronsted acids and anions deposited on oxide supports such asZrO₂ /SO₄ can be cited. These solids lead to the production of branchedisoparaffins but suffer from several major faults, among which the useof often very high isobutane/olefin molar ratios to limit the magnitudeof secondary reactions and the poor stability of the catalytic activity(inhibition of the catalyst by deposition of unsaturated oligomers) canbe cited; these catalysts therefore have to be frequently regenerated.Moreover, the weak acidity of certain acid solids, such as molecularsieves, for example, necessitates the use of high reaction temperatures,which is prejudicial to obtaining hydrocarbons with a high octanerating.

European patent application EP-A-0539277 describes a catalyst containingsilica and a solid acid phase comprising sulphuric acid; the silicaaccording to said patent application is such that its porous volume isbetween 0.005 and 1.5 cm³ per gram and its specific surface is between0.01 and 1,500 m² per gram. Said acid phase can if required contain anadditive selected from the group formed by H₃ PO₄, B(OH)₃, BF₄ H, FSO₃H, CF₃ CO₂ H, SbF₅, CF₃ SO₃ H and SO₃.

French patent application FR-A-2 687 935 describes a catalyst containinga silica with a specific surface of between 0.01 and 1,500 m² per gramand a total porous volume of between 0.005 and 1.5 cm³ per gram and anacid phase in solid state containing at least sulphuric acid andsulphuric anhydride, the silica having been impregnated with said acidphase. Said acid phase may possibly contain boric acid B(OH)₃, thecontent by weight of boric acid being between 0.01% and 50%.

SUMMARY OF THE INVENTION

The present invention relates to a catalyst comprising silica and anacid phase comprising sulphuric acid and the compound HB(HSO₄)₄, thesilica having been impregnated with said acid phase, said catalyst beingsuch that it is composed substantially of particles with an averagediameter of between 0.1 and 30 μm (1 μm=10⁻⁶ m) and preferably between 5and 30 μm such that the silica, before its impregnation with said acidphase, has a total porous volume of between 0.1 and 0.6 cm³ per gram,preferably between 0.1 and 0.4 cm³ per gram, and such that said acidphase contains (in % by weight) between 0.4 and 68.8%, preferablybetween 0.4 and 60% of the compound HB(HSO₄)₄ and between 31.2 and99.6%, and preferably between 40 and 99.6% of the compound H₂ SO₄, saidacid phase being characterised by the fact that it contains neithersulphuric anhydride (SO₃) nor boric acid [B(OH)₃ ].

In particular, said acid phase does not contain non-associated sulphuricanhydride, that is to say not having reacted with the boric acid, nornon-associated boric acid, that is to say not having reacted with thesulphuric anhydride.

The content by weight of said catalyst in acid phase is generallybetween 1 and 40%, preferably between 1 and 30%.

The invention also relates to the preparation and use of said catalystin catalytic alkylation of at least one isoparaffin selected from thegroup formed by isobutane and isopentane (that is to say isobutaneand/or isopentane: isobutane, or isopentane, or isobutane andisopentane) in the presence of at least one olefin with 3 to 6 atoms ofcarbon per molecule.

The catalyst according to the present invention leads, in a surprisingmanner, to improved catalytic performance with respect to thosedescribed in European patent application EP-A-0539277 and also withrespect to those described in French patent application FR-A-2 687 935.

The compound HB(HSO₄)₄ contained in the acid phase of the catalystaccording to the invention can be obtained by all the methods known tothe man skilled in the art. For example, and in a non-limiting manner,the preferred method according to the invention can be cited, whichinvolves reacting 1 mol of boric acid B(OH)₃ with 3 mols of sulphuricanhydride SO₃ and 1 mol of sulphuric acid H₂ SO₄ to obtain 1 mol of thecompound HB(HSO₄)₄.

The silica as a support can contain impurities such as, for example,oxides, alkalines, alkaline-earths, aluminium compounds or any otherimpurities known to the man skilled in the art, the total quantity ofthe impurities generally not exceeding 2% by weight of the silica.

The silica is generally such that, before its impregnation with saidacid phase, its specific surface is between 0.1 and 1,500 m² per gram.Moreover, said silica is generally constituted substantially ofparticles with an average diameter of between 0.1 and 30 μm, preferablybetween 5 and 30 μm.

The acid phase generally occupies between 80 and 100% of the totalporous volume of the silica, preferably between 90 and 100% of saidporous volume.

The process for preparation of the catalyst according to the inventiongenerally comprises at least two stages. In a first stage the silica iscalcined at a temperature greater than 50° C., preferably greater than80° C. and even more preferably between 150° and 600° C., for exampleequal to approximately 500° C. The duration of this calcination stage isnormally between 10 minutes and 50 hours, preferably between 15 minutesand 25 hours. The calcination is generally carried out in the presenceof dry air or a dry air/nitrogen mixture, at a rate of between 0.001 and10 liters per hour per gram, preferably between 0.1 and 5 l/h/g. Thesecond stage consists of impregnation of said calcined silica with saidacid phase. Any of the techniques well known to the man skilled in theart can be used to carry out this stage. A stage of preparation of theacid phase, prior to the impregnation stage can be added to this processof preparation.

The catalyst according to the invention thus prepared has not beensubjected to any calcination subsequent to the impregnation stage. Whenit is used in the alkylation of isoparaffin(s) by at least one olefin,it is not subjected, prior to its use, to any calcination and thusbetween the impregnation stage and said use, it is not subjected to anycalcination. The catalyst according to the invention thus prepared istherefore immediately ready for use.

The catalyst according to the present invention is used in a processwhich allows the alkylation reaction of isoparaffin by at least oneolefin to be carried out in the best conditions. In particular saidreaction being characterised by strong exothermic reaction(approximately 83.6 kJ per mol of transformed butene, if the olefin isbutene and if the isoparaffin is isobutane), the use of the catalystaccording to the present invention allows a good temperature homogeneityand concentration of reactants to be obtained.

In the process of alkylation of isoparaffin(s) using the catalystaccording the present invention, the operating conditions, and moreparticularly the temperature and pressure, are generally selected in amanner such that the mixture constituted by the isoparaffin(s), theolefin(s) and the reaction products is liquid. Moreover, it is importantthat the catalyst is immersed in said liquid in order to ensure thatthere is a good liquid/solid contact.

The catalyst according to the invention is advantageously used in thereaction zone of alkylation of isobutane and/or isopentane with at leastone olefin comprising 3 to 6 carbon atoms per molecule, in a liquidphase and in a mixture together with isoparaffin or a mixture ofisoparaffins. The catalyst according to the invention can be used in anexpanded bed, in an almost perfectly agitated reaction zone, orcirculating bed, and is preferably used in a process which uses acontinuous liquid phase, the catalyst being used in the form of asuspension, for example, according to the two implementations describedhereinafter.

In the case where the catalyst is used in the form of a suspension, in afirst implementation a reaction zone with an almost perfect mix can beused, that is to say with a perfect mix or near-perfect (agitated orGrignard vessel), using at least one agitation means, for example bymeans of a helix, in order to obtain sufficient agitation of thecatalyst in suspension in the hydrocarbonated liquid phase, whichconsists generally of isoparaffin (isobutane and/or isopentane), atleast one olefin, possibly at least one inert dilutant (for example,propane and normal butane) and the products of the alkylation reaction.The charge to be convened, composed of isobutane and/or isopentane andat least one olefin can be, for example, introduced in a liquid form atat least one point within the hydrocarbonated liquid phase present inthe reaction zone.

A second implementation of the catalyst according to the presentinvention in suspension in a hydrocarbonated phase is the cocurrent flowfluidized bed or circulating bed. In this implementation the catalyst insuspension in the hydrocarbonated liquid phase, generally consisting ofisoparaffin (isobutane and/or isopentane), at least one olefin, possiblyat least one inert dilutant (for example propane or normal butane) andthe products of the alkylation reaction, circulate from bottom to top inthe reaction zone. The group constituted by the suspension of thecatalyst in the hydrocarbonated phase then circulates through at leastone heat exchanger and at least one pump, before being introduced againat the entrance to the reaction zone. The charge to be converted,constituted by isobutane and/or isopentane and at least one olefin isintroduced either in liquid form or in gaseous form at at least onepoint in the reaction zone.

In the two types of implementation previously described, isoparaffin(isobutane and/or isopentane) not having been converted, or having beenintroduced in excess with respect to the stoichiometry of the reaction,is generally recycled after separation of the alkylate, either by directintroduction into the reaction zone or by mixing with the charge to beconverted.

The isoparaffin(s)/olefin(s) mixture is generally introduced into thereaction zone at a spatial speed per hour, expressed in weight of olefinintroduced per unit of catalyst and per hour (w.p.h.) of between 0.001and 10h⁻¹, and preferably between 0.002 and 2h⁻¹. Said mixture can alsobe produced in the interior of the reaction zone. In all cases, themixture constituted in this manner is in the reaction zone underconditions of pressure and temperature such that the mixture ofhydrocarbons remains liquid on the catalyst.

The reaction temperature is generally lower than +10° C., preferablylower than 0° C. and in manner often more preferable, lower than -3° C.The pressure of the reaction zone is sufficient to maintain thehydrocarbons in a liquid state in said zone.

In order to limit secondary reactions, an excess of isoparaffin(s) withrespect to the olefin(s) can be used. By way of example, in the case ofalkylation of isobutane by a butene, the isobutane can be introducedpure in the charge or in the form of a mixture of butanes containing,for example, at least 40% isobutane. Moreover, a pure butane or else amixture of isomeric butanes can be introduced. In any case, theisobutane/butene(s) molar ratio in the charge is generally between 1 and100, preferably between 3 and 50 and in a manner often preferred,between 5 and 15.

When the nature of the catalyst and the reaction conditions and chosenjudiciously (in particular the temperature), the catalyst according tothe invention allows the production of alkylation products of at leastone isoparaffin by at least one olefin which are valuable as fuels forengines and constituents for petrol, and which consist of, for example,at least 60% mols of paraffin having 8 atoms of carbon per molecule andless than 1% mols of non-saturated compounds, the paraffins consistingof 8 atoms of carbon per molecule composed of 70 to 98% in mols oftrimethylpentanes.

Another advantage of the catalyst according to the present invention isthe possibility of alkylizing isoparaffin with mixtures of olefins with3 to 6 carbon atoms per molecule at low temperatures, where theproportion of olefins with 4 atoms of carbon per molecule is verysignificant.

The following examples illustrate the invention without thereby limitingthe scope thereof.

EXAMPLE Example 1 Preparation of catalyst 1 according to the invention

30 g of silica with a porous volume equal to 0. 15 cm³ per gram, withparticles of an average diameter equal to 18 Nm and with a specificsurface equal to 210 m² per gram is activated by drying in air at 150°C. for 12 hours. The silica thus activated is preserved in nitrogen.After this 2.97 g of boric acid is added to 100 g of sulphuric anhydridein sulphuric acid, containing 11.5% by weight of sulphuric anhydride and88.5% by weight of sulphuric acid to obtain 102.97 g of acid phase.

After the reaction of the sulphuric anhydride and the boric acid in thepresence of sulphuric acid, and respectively in molar ratios 3/1/1, anacid phase is obtained which contains the compound HB(HSO₄)₄ in solutionin H₂ SO₄ and containing 18.6% by weight of HB(HSO₄)₄ and 81.4% byweight of H₂ SO₄.

After this dry impregnation of 20 g of said calcined solid with 5.15 gof the mixture described above is carried out. The solid thus obtained,designated catalyst 1, has a content by weight of acid phase equal to20.5%. It is kept protected from humidity and in argon at -18° C.

Alkylation of isobutane by butene-1 with catalyst 1

20 g of catalyst 1 prepared according to the method described above 1 isintroduced into a glass reactor of the Fischer & Porter type with avolume of 360 ml, previously purged by argon discharge. The reactorcontaining the catalyst is then closed, then placed under low vacuum,then cooled to the temperature of -20° C.

157 cm³ of isobutane is then added to the reactor containing thecatalyst while agitating, said reactor being immersed in a cold bath at-20° C. The catalyst +isobutane system is kept agitated for 30 minutesin order to homogenize the temperature.

2 g of butene-1 is added hourly regularly for a total of 6 hours, thetemperature of the reactor being maintained at -8.5° C. for the wholeduration of the injection.

After reaction, the hydrocarbon phase is drawn off from the reactor,then the isobutane is slowly evaporated and the alkylate is collectedand analyzed by chromatography in the vapour phase. Its composition byweight is given in table 1. The olefin conversion is 100%.

Example 2 Preparation of catalyst 2 (not according) to the invention)

To prepare catalyst 2, 20 g of the same silica as used for thepreparation of catalyst 1 is used, the calcination conditions beingidentical. The solid thus activated is preserved in argon. 20 g of saidcalcined silica is then dry impregnated with 5.15 g of a solution ofacid containing 86% by weight of sulphuric acid with a titre of 99.7% byweight, and 14% by weight in trifluoromethane sulphonic acid with atitre equal to 98% by weight. The solid obtained has a content by weightof acid phase equal to 20.5%. It is kept protected from humidity and inargon at -18° C.

Alkylation of isobutane by butene-1 with catalyst 2

The test of catalytic alkylation of isobutane by butene-1 in repeatedunder the same experimental conditions as those described in example 1.The results are described in table 1.

Example 3 Preparation of catalyst 3, not according to the invention

To prepare catalyst 3, 20 g of the same silica as used for thepreparation of catalysts 1 and 2 is used, the calcination conditionsbeing identical. The solid thus activated is preserved in argon. 20 g ofsaid calcined silica is then dry impregnated with 5.15 g of sulphuricacid with a titre of 100% by weight. The solid obtained has a content byweight of acid phase equal to 20.5%. It is kept protected from humidityand in argon at -18° C.

Alkylation of isobutane by butene-1 with catalyst 3

The test of catalytic alkylation of isobutane by butene-1 is repeatedunder the same experimental conditions as those described in examples 1and 2. The results are described in table 1.

                  TABLE 1                                                         ______________________________________                                                             Catalyst 2  Catalyst 3                                   Alkylate  Catalyst 1 (not according                                                                            (not according                               composition                                                                             (according to                                                                            to the      to the                                       (% by weight)                                                                           the invention)                                                                           invention)  invention)                                   ______________________________________                                        C.sub.5 -C.sub.7 %                                                                      5.9        10.2        12.1                                         C.sub.8 % 86.2       78.5        71.8                                         C.sub.9.sup.+  %                                                                        7.9        11.3        16.1                                         ______________________________________                                    

This table shows the advantage of working with a catalyst according tothe invention, containing an acid phase composed of sulphuric acid andthe compound HB(HSO₄)₄.

We claim:
 1. A catalyst containing silica and an acid phase comprisingsulphuric acid and HB(HSO₄)₄, the silica having been impregnated withsaid acid phase and said catalyst being such that it consistsessentially of particles with an average diameter of 0.1 to 150 μm, suchthat the silica, prior to its impregnation with said acid phase, has atotal porous volume of 0.1 to 0.6 cm³ per gram, said acid phasecontaining (in % by weight) 0.4% 0.4% to 68.8% of HB(HSO₄)₄ and 31.2% to99.6% of H₂ SO₄, and said acid phase not containing sulphuric anhydrideor boric acid.
 2. A catalyst according to claim 1 consisting essentiallyof particles of average diameter of 5 to 30 μm.
 3. A catalyst accordingto claim 1, wherein the content by weight of acid phase of said catalystis 1 to 40%.
 4. A process for the preparation of the catalyst accordingto claim 1, comprising calcining the silica at a temperature greaterthan 50° C. for a duration of 10 minutes to 50 hours, and impregnatingsaid calcined silica by said acid phase.
 5. A process according to claim4 in which the compound HB(HSO₄)₄ is obtained by reacting 1 mol of boricacid with 3 mols of sulphuric anhydride and 1 mol of sulphuric acid. 6.A process for catalytic alkylation of at least one isoparaffin selectedfrom the group consisting of isobutane and isopentane with at least oneolefin containing 3 to 6 carbon atoms per molecule, said processcomprising subjecting said isoparaffin and olefin to alkylationconditions in the presence of a catalyst of claim 1, in which processthe reaction temperature is lower than +10° C. and the pressure of thereaction zone is sufficient to maintain the hydrocarbons in liquid statein said zone.
 7. A process according to claim 6 in which the catalyst isused in a near-perfect mix reaction zone.
 8. A process according toclaim 6 in which the catalyst is used in a cocurrent flow fluidized bed.9. A catalyst according to claim 1, wherein the total process volume ofthe silica prior to impregnation is 0.1 to 0.4 cm³ /g.
 10. A catalystaccording to claim 1, wherein the acid phase contains 0.4 to 60% byweight HB(SO₄)₄.
 11. A catalyst according to claim 1, wherein the acidphase contains 40 to 99.6% by weight H₂ SO₄.
 12. A catalyst according toclaim 1, wherein the content by weight of acid phase of said catalyst is1 to 30%.
 13. A catalyst according to claim 1, wherein the acid phaseoccupies 80-100% by weight of the total porous volume of the silica. 14.A catalyst according to claim 1, wherein the acid phase occupies 90-100%by weight of the total porous volume of the silica.